Throughout history, infectious diseases were a leading cause of premature human death. In the 20th century, social improvements, antimicrobial chemotherapy and immunization led to a brief period in which infectious diseases were viewed as torments of the past. However, the emergence of new infectious agents and the reemergence of old diseases demonstrated that continued awareness, research and development are necessary to limit the impact of infectious diseases on human health. Tuberculosis (TB) is still the second leading cause of human death from an infectious disease. The emergence of drug resistant strains of Mycobacterium tuberculosis (Mtb) threatens the success of TB control programs worldwide. New drugs are needed to effectively treat patients suffering from drug resistant TB and to prevent the spread of drug resistant Mtb. Functional genomics studies identified many genes that are essential for growth of Mtb but are not targeted by current antibiotics. The long term goals of this proposal are to improve genetic tools for drug target validation and to analyze essential respiratory genes of Mtb.